1. Statement of the Invention
The invention pertains to the cagB and the cagC genes of Helicobacter pylori and to the antigenic polypeptides encoded by the genes, as well as methods of using the genes and polypeptides to diagnose H. pylori infection and predisposition to peptic ulceration and other diseases associated with H. pylori infection.
2. Background Art
Helicobacter pylori was first isolated in 1983 from gastric biopsy specimens of patients with chronic gastritis (1). A wide body of evidence, from studies that include human volunteer challenges, animal models and treatment with antimicrobial agents, indicates that H. pylori plays a critical and necessary role in the pathogenesis of chronic superficial gastritis (2). This condition remains asymptomatic in most infected persons but considerably increases the risk of peptic ulcer (3,4) and gastric adenocarcinoma (5-8). Treatment of patients with peptic ulcers with antibiotics to eradicate H. pylori infection results in ulcer healing and markedly reduced ulcer recurrence rates (9).
Pathogenic mechanisms of H. pylori are poorly understood, but the existence of ulcerogenic strains of this bacterium may explain why only a minority of patients harboring the organism develop duodenal ulcer disease. Two virulence factors produced by 50-60% H. pylori of strains are (A) a secreted cytotoxin that induces vacuolation in eukaryotic cells (10,11) and (B) a high molecular weight (120-140 kDa) superficial protein the CagA antigen (12-16). From 88-100% of H. pylori strains that have been isolated from patients with duodenal ulceration possess CagA antigen whereas in patients with superficial gastritis alone, the prevalence is 50-60%. Recent in vivo studies using gastric biopsies from patients infected with H. pylori have shown that CagA.sup.+ strains induce significantly greater interleukin-1 alpha, interleukin-1 beta and interleukin-8 production than CagA negative strains (17). Further, in vitro studies have also shown that CagA.sup.+ strains induce greater levels of proinflammatory cytokines (interleukin-8) by gastric epithelial cells than CagA.sup.- strains (18).
However isogenic cagA.sup.- mutants induce similar cytokine levels as do the wild-type strains, indicating that whereas CagA is a marker for increased inflammation, its presence is not necessary (27). Because so little is known about the pathogenesis of H. pylori, there is a need to identify other genes present exclusively in wild type cagA.sup.+ strains.
The invention identifies two genes (cagB and cagC) that are present exclusively in CagA positive H. pylori strains and can encode 36 and 101 kDa proteins. The present data show that these genes are highly associated with duodenal ulcers, and that mutants deficient in these genes do not stimulate epithelial cells to produce the pro-inflammatory cytokine IL-8.